<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #res {
            width: 220px;
            height: 100px;
            border: 1px solid red;
        }
    </style>
</head>

<body>
    <button>dianji</button>
    <div id="res"></div>
</body>

</html>
<script>
    const btn = document.getElementsByTagName('button')[0];
    const res = document.getElementById('res');
    btn.addEventListener('click', function() {
        const xhr = new XMLHttpRequest();
        //加一个参数，参数会让每一次的头文件都不一样
        xhr.open("GET", 'http://127.0.0.1:8080/server?t=' + Date.now());
        xhr.send();
        xhr.onreadystatechange = function() {
            if (xhr.readyState === 4) {
                if (xhr.status >= 200 && xhr.status < 300) {
                    res.innerHTML = xhr.response;
                }
            }
        }
    })
</script>